(1) Field of the Invention
The present invention relates to a method for a non-contact optoacoustic communications downlink from an in-air platform to a submerged platform.
(2) Description of the Prior Art
In the present art, underwater acoustic telemetry involves a situation of all in-water hardware to establish a communications link. Currently, a method of communications does not exist between an in-air platform to a submerged platform at speed and depth.
In the past and without the aid of buoys, submergible platforms would have to surface to receive high data rate communications from an in-air platform and be able to transmit data to an in-air platform or remote site. Alternatively, the submergible and/or in-air platforms would have to leave behind transmit buoys (ceramic-based transducers that must be submerged for efficient coupling of acoustic energy into the water). These communication procedures can be time-consuming and inefficient.
The ability to generate underwater acoustic signals from a remote, aerial location using a high energy pulsed infrared laser has been demonstrated. The laser beam is directed from the air and focused onto the water surface, where the optical energy is converted into a propagating acoustic wave. An early attempt to control the laser-generated acoustic spectrum via a two unit CO2 laser pulse system has been demonstrated.
Laser light incident on an absorbing material such as water produces sound relating to the physical nature of the interaction. In the linear regime, methods of communication have been considered in little detail due to the low conversion efficiency. However, in the non-linear regime, narrowband communication schemes do not exist at all and for that matter little has been done with closely spaced time sequential multiple pulses for any application.
In the late 1970s, the Soviet researcher Lyamshev and in the late 1980s, Berthelot studied the use of pulse train laser intensity modulation for communications in the linear regime where the laser absorbing material is water. It was shown theoretically that an impulse train is the most efficient method of concentrating energy at a tonal location given the constraint of equal energy. However, at that time and to this day, it is more efficient with commercially available lasers with power and energy limitations to use long pulse continuous wave intensity modulated laser beams for optoacoustic sound generation of specific acoustic tonal frequencies.
It is also known in the art that non-linear optoacoustics demonstrate the potential to create useful acoustic signal levels. It has been theoretically shown that a laser pulse repetition rate can be used to control the spectrum of the generated optoacoustic signal in the non-linear optoacoustic regime. Also, the laser wavelength and laser pulse duration used can determine the acoustic transient effects which occur subsequent to the initial optical breakdown induced shock wave transient. The cavitation bubble size determines the acoustic frequency that can be generated since the bubbles can oscillate at these frequencies.
As such, a need exists for a system and method of use, which utilizes a pulse repetition laser and a non-linear regime to enhance optoacoustic communication between an in-air platform (i.e. aircraft) and a submerged platform.
The key advantages are that such a system would employ a non-contact, covert, optical method to provide greatly enhanced communications and remote active transmission capabilities that do not currently exist and that solve mission problem areas, eliminating the need to employ non-disposable tethered sound sources from the air or disposable resources such as sonobuoys.